An equation for the dose response of radiation-induced apoptosis: possible incorporation with the LQ model.

Based on in vitro and in vivo data, we proposed an equation to describe the dose response of radiation-induced apoptosis. This equation can be incorporated into the LQ model to account for the contribution of apoptosis-mediated cell death in clonogenic survival curve. The modified LQ equation is a composite of the dose responses of two subpopulations, one susceptible and the other resistant to apoptotic cell death. For the apoptosis-resistant fraction, the size of which varies for different biological systems, the conventional LQ relation applies. For the susceptible subpopulation, the LQ equation is modified by e-zeta D, a functional form consistent with the observed dose-rate independence of this mode of cell death.